1. Field of the Invention
The present invention relates to a continuous variable valve timing device and, more particularly, to an oil circuit for a continuous variable valve timing device.
2. Description of Related Art
A dual continuous variable valve timing (CVVT) device makes it possible to continuously regulate lift timing of intake and exhaust valves according to the operation state of an engine, thereby improving output of the engine, reducing harmful components of exhaust gas, and increasing fuel efficiency.
Responsiveness and operation of the CVVT device are ensured depending on whether or not hydraulic pressure of oil fed by an oil pump reaches an optimal time of point and is continuously transmitted. At this time, in the structure that simultaneously controls two variable mechanisms, i.e. intake and exhaust valves, a hydraulic circuit is required not only to be free from variation in hydraulic pressure if possible but also to be connected in parallel to one passage. Further, in order to drive a cam in cooperation with a crank, the cam must interact with the crank by means of a chain or a belt. In this case, tension of the chain or the belt transmitting a driving force must be also regulated.
In detail, in order to properly realize the CVVT device, hydraulic pressure applied to two cam shafts must be uniformly supplied and ensured to a predetermined level or more. If not so, malfunction caused by a time difference cannot be prevented. In order to accurately cooperate with the crank, the tension of a driving force transmitting means such as a belt or a chain must be simultaneously regulated even the moment the CVVT device is operated.
FIG. 1 illustrates an oil circuit for a conventional continuous variable valve timing (CVVT) device.
Referring to FIG. 1, the oil circuit for a CVVT device includes a main oil passage 120 disposed from a cylinder block toward a cylinder head and guiding oil fed from a main gallery 110, and an oil circuit 160 disposed on a side of the cylinder head to feed the oil passing through the main oil passage 120 to the CVVT device 150 by way of an oil filter 130 and an oil control valve 140.
However, the conventional CVVT device has problems in that, since the oil circuit 160 is disposed on the cylinder head side, the oil cannot be fed to a timing chain tensioner 170 in a non-CVVT device that is free of the oil circuit, and that, since the oil is separately fed to the cam shafts, the cooperation between the crank and the cam is correctly performed.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.